System for depositing and protecting sand on the floor of a sea, or other body of water

ABSTRACT

This invention relates to a system for depositing and protecting sediments on the floor of a body of water by utilizing an arch-shaped rigid cast sheet of heavy material with the weight thereof being utilized to maintain the sheet in bridging relationship to a pipe or like installation resting on the floor of the body of water. Alternatively, several of such sheets can be interlocked to each other by tongues and grooves, may be pivotally secured to each other or to the pipe, and are provided with means for precluding damage to the pipe should the sheets be gripped or contacted by a dragging anchor of a vessel.

The invention relates to a system for depositing and protecting sand andother littoral drift material on the floor of a sea, lake, river orother body of water.

Various kinds of barriers exist or have been proposed in the form ofgroins, breakwaters, and the like. But all of them are so deficienttechnically or aesthetically, and/or so expensive that coastalprotection on a sufficiently large scale so far has been out of thequestion.

The system in claim 1 combines technical perfection with very low cost,allowing for large scale coastal protection. By placing the device withits longitudinal direction perpendicular to the coast, an effectcomparable with that of a natural submarine reef is obtained. Thestreamlined cross-section, the flat slopes and properly proportionedapertures make up a device that traps the drifting sediment and protectsit from scouring. Thereafter deposition of sediment on top and alongboth sides of the device gradually builds up a shoal extending far awayfrom the device in all directions. Like natural reefs this shoalrefracts the waves and spreads their energy. By building such headlandsat suitable intervals a stabilization of a whole coastline can beachieved.

Besides for coastal protection the system may be used for otherpurposes, e.g. prevention of siltation in navigable channels and harbourmouths. In such cases the device is placed along the channel or theharbour mouth on its both sides, thereby forming a hindrance for passageof the drift materia Being completely submerged this device does notdisfigure the coast, opposite the traditional groins, breakwaters, etc.

Another field of application is protection from undermining of lengthyhydraulic structures such as submarine pipelines, cables, foundationsand the like. In this case the device is placed on top of the structureto be secured and thereby causes an accumulation of sediment along bothsides of the structure.

The description will be illustrated by reference to the drawings inwhich:

FIG. 2 is a plan view of corrugated plates 1 assembled by shapes 8 andsupported on angled shapes 9 and anchored to discs 6 through ropes 7;

FIG. 7 is a cross-section taken along the line I--I of FIG. 1;

FIG. 3 is a plan view of a perforated sheet 2 assembled by longitudinalshapes 4 and supported on lattice trusses 10 and anchored to discs 6through ropes 7;

FIG. 4 is a cross-section taken along the line II--II of FIG. 3;

FIG. 5 is a cross-section of a perforated sheet 2 assembled bylongitudinal shapes 4 and supported on rope forming a lacing 11stretched by 3 struts 12 in hinged interconnection in one point at themiddle;

FIG. 6 is a plan view of a perforated sheet 2 assembled by longitudinalshapes 4 and reinforced by zig-zag wire ropes 18 and supported oninflatable spheres 13 and anchored and stretched by discs 6 throughanchoring ropes 7;

FIG. 7 is a cross-section taken along the line III--III of FIG. 6;

FIG. 8 is a plan view of a perforated sheet 2 assembled by longitudinalshapes 4 and supported on lattice trusses 14 consisting of twosymmetrical halves which are interconnected at a point above thepipeline or other structure 15 which is to be protected from scour;

FIG. 9 is a cross-section taken along the line IV--IV of FIG. 8;

FIG. 10 is a cross-section of symmetrical halves of a sheet 3 supportedby longitudinal shapes 4 on crossbeams 16 that are attached directly andthrough props 64 to clutches 17 which are tightened around the pipeline15 by excentrics 65 mounted on the clutches 17;

FIG. 11 is a cross-section of an impermeable sheet 3 containingapertures along its ridge and supported by longitudinal shapes 4 onpairs of shapes 26 that are in mutually hinged connection over the topof the structure 15 which is to be protected; the outer ends of 26 beingsupported on and anchored by poles 5 mounted on discs 6;

FIG. 12 is a plan view of an impermeable sheet 3 containing apertures 25at the ridge and assembled by longitudinal shapes 4 and reinforced byzig-zag wire ropes 18 and supported on the pipeline 15 via inflatablespheres 13 and anchored by discs 6 through anchoring ropes 7 and poles5, and stretched and prevented from flapping up and down by discs 6through ropes 7;

FIG. 13 is a cross-section taken along the line V--V of FIG. 12;

FIG. 14 is a side view of a pipeline supplied with a folded deviceconsisting of a flexible sheet, e.g. an open net 2, the center portionof which is fixed along the top of the pipeline, and both edges of whichcontain a longitudinal pipe for stretching and holding the sheet. Eachsupporting cross-beam 55 is hinged by one end to a clamp that is placedin the concrete coating of the pipeline or round the pipeline. In thisfolded position the cross-beams two and two are held together by ties orclamps 56. Supplied with rings around the cross-beams 55 or slidersrunning in a longitudinal groove in each cross-beam, the sheet can befolded tight to the pipeline;

FIG. 15 is a cross-section taken along the line VI--VI of FIG. 14;

FIG. 16 is a cross-section of the device shown in FIGS. 14-15 whenunfolded on the seabed;

FIG. 17 is a plan view of a segment of a sheet 34 shaped to form conicalchannels 35;

FIG. 18 is a cross-section taken along the line VII--VII of FIG. 17;

FIG. 19 is a plan view of a segment of a sheet 36 containing slits 37and folds 38;

FIG. 20 is a cross-section taken along the line VIII--VIII of FIG. 19;

FIG. 21 is a plan view of a segment of a sheet consisting of severallayers of mesh 40;

FIG. 22 is a cross-section taken along the line IX--IX of FIG. 21;

FIG. 23 is a vertical cross-section of an auger-formed disc 41 screwedinto the ground by means of a detachable rod 42, the anchoring rope 7 inthis case being fastened directly on to the disc 41;

FIG. 24 is a side view of an anchoring disc 41, to the center rod 43 ofwhich the anchoring rope 7 is fastened via a rotating reaction ring 44;

FIG. 25 is a side view of a pipe 42 for conducting a water jet throughthe hole 31 of the disc 6 which is being pressed against the lower endof 42 and its two feet 27 by means of a neoprene ring 46, which has beenput through the hole 32 of the disc 6, retained by a crosspiece 33,stretched and thereafter suspended from the hook 28 mounted on the clamp29, the clamp 29 in this case being supported by the nut 30 fitting intoscrew thread on the outer surface of 42 allows for lowering of 29 afterthe positioning of 6, so that the upper end of 46 can be moved from 28to the device to be anchored, and 42 be removed;

FIG. 26 is a cross-section taken along the line X--X of FIG. 25;

FIG. 27 is a cross-section of an embodiment consisting of a corrugatedplate 1 with rounded and perforated ridge and stiffened by longitudinalshapes 8 and by ties 45 and anchored by discs 6 through stretchedneoprene anchoring ropes 46;

FIG. 28 is a cross-section taken along the line XI--XI of FIG. 29;

FIG. 29 is a plan view of an open box-type anchor 51 supplied withhorizontal bars 52;

FIG. 30 is a cross-section of a device made of concrete stiffened byties 45;

FIG. 31 is a plan view of a concrete element primarily for protection ofcables or small diameter pipelines; it is provided with holes 68 at thetop;

FIG. 32 is a large-scale cross-section taken along the line XII--XII ofFIG. 31;

FIG. 33 is a large-scale cross-section taken along the line XIII--XIIIof FIG. 31;

FIG. 34 is a large-scale cross-section taken along the line XIV--XIV ofFIG. 31;

FIG. 35 is a plan view of a pipeline 15 protected by concrete elements61 or 62 which contain channels 58 and are supported on the pipeline bymeans of clamps 59. The edges of the elements are formed with tonguesand grooves 66, so that the elements form a continuous, coherent sheeton both sides of the pipeline,

FIG. 36 and FIG. 37 are alternative cross-sections taken along the lineXV--XV of FIG. 35;

FIG. 38 is a plan view of the base of a special type of drilling rig;and

FIG. 39 and FIG. 40 are alternative large-scale cross-sections takenalong the line XVI--XVI of FIG. 38.

The ridge formed by the meeting of the two side portions should berounded (FIGS. 4, 9, 10, 16, 27, 30, 32, 36, 37). The two side portionsshould not be too steep. To obtain the desired depositing effect and toprevent too heavy strain of the sheet, the surface of the side portionsshould not be steeper than about 1:4 -- 1:3. The angle of slope maydecrease gradually from the middle toward the edges of the device, toprevent local scour at the edges (FIGS. 13, 27, 30).

The device may be made of more or less flexible material. Rigidmaterials such as concrete, steel, aluminium, glassfiber-reinforcedpolyester or polyethylene are appropriate where the vertical componentof the orbital motion of the waves is significant. To increase thestiffness and strength, sheet material may be corrugated (FIGS. 1-2,27). The corrugation may be orientated parallel with or perpendicular tothe lateral direction of the device. To avoid creation of turbulence,the surface of the top of the sheet should be even, without corrugation.

Suitable flexible materials are for example polyethylene, polyester,nylon, or natural fibers such as jute and sisal.

Depending on the purpose of the device and the prevailing conditions,the sheet may be impermeable, it may be provided with apertures locatedat the top of the ridge (FIGS. 1-2, 10, 27, 30), or a part of or all ofthe surface of the device may be perforated evenly or differentiatedly.

The sheet may consist of two or more separate layers of perforatedmaterial. If the percentage area of the apertures is rather small, theupward flow through the apertures at the leeside of the device herebycan be increased. In such case the upper layer(s) may be very flexibleand a little wider or longer than the lower layer and be fastened tothis in certain points only, so that it can rise a little distance abovethe lower layer for upward flow. If, on the other hand, the sheetconsists of open net material (FIGS. 21-22), so that it cannot retainthe particles of the sediment, the extra, larger layer(s) of net may beattached at certain points to the underside of the upper, stretchedlayer of net, and preferably be made of bouyant material. The upwardflow will press the lower layer(s) against the upper layer, whereby thesediment will be prevented from passing through the nets.

The same effect as obtained with such extra layers of net can beachieved by a sheet consisting of open net that is supplied on itsupper- respectively underside with strips of bouyant, flexible materialattached by one end to the surface.

To prevent local scour under the edges of the device, the percentagearea of the perforation may increase gradually from the ridge toward theedges of the device. In practice such gradual differentiation may bereplaced by joining several layers of perforated sheets together andstepping down the number of layers toward the edges.

In particular in devices for protection of submarine structures, anopening along the ridge (FIGS. 1-2, 10-11) may be the only aperture ofthe device. It may be obtained by spacing the two interconnected sideportions apart.

To prevent the coarser part of the sediment from becoming conducted upthrough the apertures, these may be covered with strainers made, forinstance, of nylon mesh.

With the aims of increasing the rate of deposition of sediment and ofpreventing overloading of the device due to the impact of waves or dueto deposition of sediment on top of the device, the sheet may be formedof sediment on top of the device, the sheet may be formed in specialways: The apertures may be provided with sheltering pockets 38 (FIGS.19-20) which prevent the current above the device from passing downthrough the apertures 37, but allow for falling down of sedimentdeposited on the device. The pockets 38, made of flexible or stiffmaterial, may be attached to the surface or be formed in the sheetitself by slitting and folding it up like the raised teeth of a shredder(FIGS. 19-20), if necessary stiffened by attached forms. The pockets maybe placed on the top side and/or the underside of the sheet.

In some cases the object is, on the contrary, to accumulate a load ofsediment on the device in order to keep the edges of the device tight tothe floor. This may be achieved by means of pockets attached to thedevice, without perforation underneath the pockets.

The sheet may be shaped to form conical channels 35 with upwardly ordownwardly decreasing cross-sectional area (FIGS. 17-18), or the sheetmay have a grid structure with vertical and/or slanting sidewalls.

The build up underneath the device may be accelerated by a successiveregulation of the effective flow area of the perforation. For example,in a device as shown in FIGS. 10, 11 or 13 it may be appropriate tostart with a comparatively large flow area at the top of the device,allowing for a filling up of the hollow underneath the device within aminimum of time. When the hollow is almost filled, part of the aperturesmay be closed - e.g. by means of strips of flexible or stiff materialattachable to the surface of the sheet - so that the depositionthereafter can grow all the way up to the underside of the sheet.

The join of the widths of material making up a flexible sheet may bemade in several ways. In cases of staying of the sheet by means of rigidlongitudinal and/or cross-stays 4 for prevention of flapping up and downof the sheet, the stays may be placed in sleeves made in the sheetmaterial (FIGS. 9-13), or they may be formed as assembling bars 4joining neighbouring widths together. For this purpose two oppositesides of each stay may contain a groove which embraces the bended edgeor a bead molded in the edge of the width of sheet material.

A sheet may be supported in numerous ways. Its ridge may be supported onvertical poles drive, water-jetted, screwed or vibrated into the ground.Each pole may be mounted on a horizontal disk to increase the supportingarea and serve as anchor. In case of water-jetting, the pole consists ofa pipe, and the disk is perforated at its center, so that the water canbe jetted through the pipe. In case of screwing, the disk is shaped asan auger with one turn.

A flexible sheet 2 as shown in FIGS. 6-7 may be supported at its middleby inflatable spheres 13 or by a continuous inflatable hose, allowingfor a convenient way of installing the system and maintain a perfectstretching of the sheet under all conditions.

Devices protecting submarine structures such as pipelines, cables,foundations, and the like, may be supported directly on the structure(FIGS. 10, 39) or via spheres 13 (FIGS. 12-13) or via a continuous hose.

The side portions may be supported on lattice girders (FIGS. 3-4, 9)made of such materials as steel, aluminum or glassfiber-reinforcedpolyester. A special design is shown in FIG. 5. The three points of askeleton consisting of three rigid members 12 are connected by a rope 11on which the sheet 2 is supported. By the use of rope instead of rigidmembers, bending forces are avoided.

In systems protecting submarine structures (FIGS. 9-13) the girders mayconsist of two symmetrical halves supported at the middle of thestructure (FIGS. 10-11) or on each other a distance above the structure(FIG. 9). To prevent any flapping up and down of the sheet, tethering 7(FIG. 12) of intermediate points of the sheet may be necessary.

In cases where the bending moments are not too great, the latticegirders may be replaced by beams 16 or 26 (FIGS. 10-11). Where thevertical motions of the water are ignorable, e.g. at great depths ofwater, no support of the side portions may be required (FIGS. 6-7,12-13).

Due to their weight, devices made of concrete normally need noanchoring. Small devices such as elements for protection of cables andsmall diameter pipelines, FIGS. 31-34, are easily handled by the divers.To enhance the stability of the elements they may be interlocked bymeans of tilted end surfaces 19-22 and/or tongues 23 and grooves 24.

Larger devices of concrete, FIGS. 35-37, require utilization of bouyancyto enable the divers to handle them under water. Appropriately, eachelement 61 or 62 contains a system of interconnected air-filled channels58 making up such portion of the total volume that the element isweightless under water. If necessary, lightweight concrete may be used.During the installation, the channels 58 are closed by a valve or a corkclosing the one or two holes connecting outwardly the system ofchannels. When the elements are in place, the valves are opened,respectively the corks removed, so that the channels become filled withwater.

Alternatively, water-absorbent lightweight concrete with or withoutchannels may be used. For instance, the surface of each element mayconsist of water-tight concrete, whereas the interior of the plateconsists of lightweight concrete that is only connected outwardlythrough one or two openings that can be closed. Or the plate consistsexclusively of absorbent lightweight concrete, the surface of whichduring the installation is covered by a detachable sheet of impermeableplastic.

A system consisting of open net (FIGS. 21-22) needs only littleanchoring. FIGS. 28-29 show an anchor to be fixed to the lower ends ofthe cross-girders 9, 10, 14, 16 or 26, or to the edges of the sheet. Itconsists of a flat, circular or angular box 51 which is open at itsupper end so that it will become filled with the drifting sediment.Level with its bottom its periphery may be supplied with horizontal bars52 to resist upheaval through the bed sediment when the box has beenundermined and sunk by the waves and currents, after having been placedon the bed.

Lighter devices made of solid materials normally have to be anchored inthe ground. The anchoring at the edges (FIGS. 6-7, 12-13) or at themiddle (FIGS. 1-5, 15, 27) may be effected by disks 6 that arewater-jetted or screwed into the ground. The disks may be connected withthe device by means of rope 7 (FIGS. 2, 4, 5, 15), or by poles 5 asdescribed above, in cases where a support of the edges of the system isrequired, e.g. because of initial scour at the edges. The rope 7appropriately is connected to the screw-anchor 41 (FIG. 24) through arotating reaction ring 44.

To keep the edges of systems as shown in FIGS. 1-5, 15, 27 tight to thefloor under all conditions, so that the currents cannot get underneaththe edges and remove the device, the rope 7 should include elastic parts46 (FIGS. 25-27), e.g. neoprene, which are stretched sufficiently toabsorb under steady tensioning any possible settlement of the device.Preferably the elastic member 46 fastened at its lower end to the disk 6should be placed and stretched by means of, possibly inside, thedetachable pipe 42 for water-jetting or screwing the disk 6 into theground. After positioning of the disk, the upper grip of the elasticmember 46 is transferred from the pipe 42 to the device, and the pipe isremoved.

To minimize the expensive underwater work, the devices should beprefabricated, so that only the anchoring has to be carried out underwater. Devices as shown in FIGS. 1-5, 27 and 30 may be assembled incomplete sections on the beach and thereafter rolled, e.g. on inflatableplastic rollers, and floated on the rollers to the site where the systemis to be installed. Here the rollers are detached, and the section sinksto the bottom where it is anchored, if necessary.

On new pipelines to be laid on the sea- or riverbed, a collapsibledevice as shown in FIGS. 14-16 may be mounted on the pipeline before itslaunch from the lay barge. The device consists of a flexible sheet 2supported by cross-beams 55 divided in symmetrical halves which arehinged by one end to clamps placed in the concrete coating of thepipeline or round the pipeline or cable. The sheet is in fixedconnection with the cross-beams and/or the pipeline along the centerlineof the device only. Along either edge the sheet contains a pipe 60 forstretching of the sheet. Supplied with rings around the cross-beams orsliders running in a longitudinal groove in each cross-beam the sheetcan be folded compactly along the centerline before the launch of thepipeline. With the cross-beams two and two temporarily tied or clampedtogether in a vertical position, the device can pass through the stingerof the lay barge, without regard to the width of the stinger. To easethe unfolding of the device when the pipeline or cable has been placedon the sea- or riverbed, a system of elastic members may automaticallyunfold the cross-beams as well as the sheet when the diver has openedthe clamps that temporarily have held the cross-beams in a verticalposition. For example, a neoprene strap 65 fixed to each pair ofcross-beams and surrounding the pipeline will unfold the beams and pressthem against the seabed, when the temporary clamps 56 are opened.Correspondingly, stretched elastic straps connecting the longitudinalpipes 60 with the outer ends of the cross-beams may automatically unfoldthe sheet when the cross-beams move from vertical to horizontalposition. The release of these straps may be effected by the impact ofthe cross-beams hitting the ground or by the movement and/or geometricalchange of the members locking the longitudinal pipes and the sheet infolded position.

Besides accumulation of sediment around a submarine structure, theobject of a system often is to prevent ships' anchors, dragnets, etc.,from catching hold of and damaging the structure. A system as shown inFIGS. 35-37 is ideal in this respect. Even if an anchor should catchhold of the lower edge of an element and even if it should be able toremove the coherent assembly of elements, the upper edge of the elementwould rise, thereby raising the anchor-chain and the anchor-shank sothat the anchor in any case would slip over the pipeline.

To cause the anchor-blade or -arms to be lifted as high above thepipeline as possible, projections 69 on the underside of the element maybe appropriate. When a removed element slides across the pipeline, andthe projection 69 reaches the pipeline, the edge of the element carryingthe anchor will be lifted further upwards, so that the blade or arms ofthe anchor are prevented from damaging the pipeline. The projections 69may be pipes embedded in the concrete or mounted through holes in theconcrete after positioning of the element.

Alternatively, such lifting of the anchor-blade or -arms may be broughtabout by corresponding projections 70 and 71. When a removed element 61or 62 slides across the pipeline, the projections 70 will reach thepipeline and then cause the element to rotate around the centerline ofthe pipeline until the former upper edge of the element reaches thesurface of the element on the other side of the pipeline. Locatedproperly in relation to 70, the projections 71 now will catch hold ofthe former upper edge of the removed element and cause the the elementto turn about this edge, thereby lifting even higher the anchor carriedby the former lower edge of the element.

A smaller device as shown in FIGS. 31-34 may turn about the edgeopposite the edge caught by the anchor or fishing gear and thereby liftthe anchorshank. To call forth such turning, the element should beprovided with downward projections to ensure sufficient resistance fromthe bed sediment. Appropriately, such projections may be obtained bycorrugating the lower edge in both sides of the element, the waves ofthe corrugation being perpendicular to the pipeline and the waveheightgradually decreasing from maximum at each edge to zero along the ridgeof the element. Alternatively, the underside of the element may beprovided with projections descending into the bed sediment, or the edgesmay end as vertical skirts, or the element may include inclined orvertical pins 69 embedded in the element or stuck into the seabedthrough holes in the element after positioning of this. In a deviceconsisting of a sheet supported by stays 4 and cross-beams 26, thesemembers may be made strong enough to carry the weight of a ship's anchorand/or the anchor-chain, whereby this device will conduct the anchorover the pipeline in the same way as the above device made of concrete.

In many cases the lengthy structure to be secured only needs protectionon one side. In such cases the exposed side of the structure isprotected by the corresponding half of the symmetrical system concerned.For example, a pipeline crossing a river only needs protection on itsupstream side, if the current is always unidirectional, and the waveaction is inessential. Similarly, a steep seawall, mole or quay may beprotected from the undermining effect of waves and currents by suchsheet.

Other special types of offshore structures to be secured include thebase structures of certain types of platforms, e.g. the type shown inFIG. 38. An appropriate device in such case includes detachable sectionsof rigid material 67, e.g. steel. They may be hinged pivotally to theedges of the foundation, so that they can rest on top of this during thetransport of the platform to a new location, and be swung down on theseabed when the foundation has reached the seafloor. To obtain theoptimum configuration of the whole, the foundation itself should beformed with a cross-section as shown in FIG. 39 or FIG. 40 to preventany undermining. A vertical skirt 50 penetrating into the seabed alongthe edges of the foundation helps prevent flow along the underside ofthe structure.

I claim:
 1. A system for depositing and protecting sediment on the floorof a body of water comprising a pair of sheets each having oppositelongitudinally extending side edge portions and opposite transverselyextending end edge portions, first and second longitudinally extendingside edge portions of a first of said pair of sheets being in contiguousrelationship to respective first and second longitudinally extendingside edge portions of a second of said pair of sheets in an inoperativeside-by-side upright position of said pair of sheets, said firstlongitudinally extending side edge portions of said first and secondsheets being disposed for pivotal movement between said inoperativeposition and an operative position at which each sheet is inclinedrelative to the floor of a body of water and defines therewith an acuteangle, and means for releasably securing said first and second sheetstogether in said inoperative position.
 2. The system as defined in claim1 wherein said first and second sheets are constructed from flexiblematerial.
 3. The system as defined in claim 2 including a plurality ofrigid transversely extending braces supporting both said flexible sheetsin at least the operative positions thereof.
 4. The system as defined inclaim 3 wherein said first and second sheets are constructed fromflexible material.
 5. The system as defined in claim 1 including meansfor pivotally securing said first longitudinally extending side edgeportions of both said first and second sheets to a installation.
 6. Thesystem as defined in claim 5 wherein said first and second sheets areconstructed from flexible material.
 7. The system as defined in claim 1including means for pivotally securing said first longitudinallyextending side edge portions of both said first and second sheets toeach other.
 8. The system as defined in claim 7 including means forclamping said first longitudinally extending side edge portions of bothsaid first and second sheets to an installation adapted to rest upon thefloor of a body of water.
 9. The system as defined in claim 7 whereinsaid first and second sheets are constructed from flexible material. 10.A system for depositing and protecting sediment on the floor of a bodyof water comprising a single rigid cast sheet of heavy material havingopposite longitudinally extending side edge portions and oppositetransversely extending end edge portions, said sheet having a centrallongitudinally extending portion between said longitudinally extendingside edge portions, said central portion having upper and lowersurfaces, said lower surface opening in a downward direction toward thefloor of the body of water, a plurality of rigid reinforcing elementsbeneath and in spanning relationship to said lower concave surface, andsaid reinforcing elements being connected to said longitudinallyextending side edge portions.
 11. A system for depositing and protectingsediment on the floor of a body of water comprising a sheet havingopposite longitudinally extending side edge portions and oppositetransversely extending end edge portions, said sheet having a centrallongitudinally extending portion between said longitudinally extendingside edge portions, said central portion having upper and lowersurfaces, said lower surface opening in a downward direction and beingadapted to opposingly overlie an installation resting upon the floor ofthe body of water, said sheet transversely spanning the installation,means projecting downwardly from each longitudinally extending side edgeportion of said sheet for preventing an anchor blade of an anchor fromcontacting and damaging the installation upon the sheet being slidacross the installation by anchor movement.
 12. The system as defined inclaim 11 wherein said projecting means are in downward divergingrelationship.
 13. The system as defined in claim 11 wherein saidprojecting means are in downwardly converging relationship.
 14. Thesystem as defined in claim 11 wherein said sheet includes hollow chambermeans for imparting bouyancy to said sheet, and means for introducingwater into said hollow chamber means.
 15. The system as defined in claim11 including a plurality of aperture means along said central portionopening completely through said upper and lower surfaces.
 16. A systemfor depositing and protecting sediment on the floor of a body of watercomprising a sheet of material having opposite longitudinally extendingside edge portions and opposite transversely extending end edgeportions, said sheet having a central longitudinally extending portionbetween said longitudinally extending side edge portions, said centralportion having respective upper and lower surfaces, said lower surfaceopening in a downward direction and being adapted to opposingly overliean installation resting upon the floor of the body of water, meansdefining integral portions of said sheet at said opposite transverselyextending end edge portions for matingly interlocking said sheet toother like constructed sheets thereby forming a sheet-to-sheet cover fora submerged installation, and means projecting downwardly from eachlongitudinally extending side edge portion of said sheet for preventingan anchor blade of an anchor from contacting and damaging a submergedinstallation upon the sheet being slid across the installation by anchormovement.
 17. A system for depositing and protecting sediment on thefloor of a body of water comprising a sheet of material having oppositelongitudinally extending side edge portions and opposite transverselyextending end edge portions, said sheet having a central longitudinallyextending portion between said longitudinally extending side edgeportions, said central portion having respective upper and lowersurfaces, said lower surface opening in a downward direction and beingadapted to opposingly overlie an installation resting upon the floor ofthe body of water, means defining integral portions of said sheet atsaid opposite transversely extending end edge portions for matinglyinterlocking said sheet to other like constructed sheets thereby forminga sheet-to-sheet cover for a submerged installation, and meansprojecting downwardly from each longitudinally extending side edgeportion of said sheet for preventing an anchor blade of an anchor fromcontacting and damaging a submerged installation upon the sheet beingslid across the pipe by anchor movement, and said projecting means beingin downwardly diverging relationship to each other.
 18. A system fordepositing and protecting sediment on the floor of a body of watercomprising a pair of sheets each having opposite longitudinallyextending side edge portions and opposite transversely extending endedge portions, a first longitudinally extending side edge portion ofeach pair of sheets being in contiguous relationship to each other, asecond longitudinally extending side edge portion of each pair of sheetsbeing in remote relationship to each other and adapted for dispositionat opposite sides of an installation resting upon the floor of the bodyof water, the opposite transversely extending end edge portions of eachsheet having respective grooves and tongues projecting and openinglongitudinally whereby like constructed sheets can be interlockedtongue-to-groove to either transversely extending end edge portions ofsaid pair of sheets, and means projecting downwardly from eachlongitudinally extending side edge portion of said sheet for preventingan anchor blade of an anchor from contacting and damaging a submergedinstallation upon the sheet being slid across the installation by anchormovement.
 19. A system for depositing and protecting sediment on thefloor of a body of water comprising a pair of sheets each havingopposite longitudinally extending side edge portions and oppositetransversely extending end edge portions, a first longitudinallyextending side edge portion of each pair of sheets being in contiguousrelationship to each other, a second longitudinally extending side edgeportion of each pair of sheets being in remote relationship to eachother and adapted for disposition at opposite sides of an installationresting upon the floor of the body of water, the opposite transverselyextending end edge portions of each sheet having respective grooves andtongues projecting and opening longitudinally whereby like constructedsheets can be interlocked tongue-to-groove to either transverselyextending end edge portions of said pair of sheets, means projectingdownwardly from each longitudinally extending side edge portion of saidsheet for preventing an anchor blade of an anchor from contacting anddamaging a submerged installation upon the sheet being slid across theinstallation by anchor movement, and said projecting means being indownwardly diverging relationship to each other.
 20. A system fordepositing and protecting sediment on the floor of a body of watercomprising a pair of sheets each having opposite longitudinallyextending side edge portions and opposite transversely extending endedge portions, a first longitudinally extending side edge portion ofeach pair of sheets being in contiguous relationship to each other, asecond longitudinally extending side edge portion of each pair of sheetsbeing in remote relationship to each other and adapted for dispositionat opposite sides of an installation resting upon the floor of the bodyof water, the opposite transversely extending end edge portions of eachsheet having respective grooves and tongues projecting and openinglongitudinally whereby like constructed sheets can be interlockedtongue-to-groove to either transversely extending end edge portions ofsaid pair of sheets, means projecting downwardly from eachlongitudinally extending side edge portion of said sheet for preventingan anchor blade of an anchor from contacting and damaging a submergedinstallation upon the sheet being slid across the installation by anchormovement, and said projecting means being in downwardly convergingrelationship to each other.